The overall objectives of this study are to determine the organization of neurons in the prevertebral ganglia, the origin, pattern and organization of synaptic input to neurons in the prevertebral ganglia and the occurrence of afferent synaptic input to these ganglia from different functional regions of the gastrointestinal tract. The areas of particular interest are: (1) the neuronal organization in the celiac plexus of the gastroduodenal inhibitory reflex in the guinea pig, (2) to determine if "pacemaker-type" neurons are present in the cat inferior mesenteric and celiac ganglia and, if so, their location and distribution, (3) the topographical distribution of noradrenergic neurons in prevertebral ganglia, (4) the pattern and organization of peripheral and central synaptic input to neurons in the cat inferior mesenteric ganglion, (5) to determine if mechanoreceptors in the wall of the colon make synaptic contact with neurons in the inferior mesenteric ganglion of the cat, and (6) the effect of polypeptide - known to occur in nerve terminal in these ganglia - on membrane properties of and synaptic input to noradrenergic neurons in guinea pig ganglia and on on-going endogenous activity in neurons in cat prevertebral ganglia. The method of approach will be the measurement in vitro of membrane properties and synaptic responses of single neurons using the intracellular recording technique. The method of approach for determining the topographical distribution of neurons in the prevertebral ganglia will be the horseradish peroxidase making technique. The prevertebral ganglia which will be studied are, in the guinea pig, the celiac ganglion and, in the cat, the inferior mesenteric and celiac ganglia.